Communication devices such as wireless devices are also known as e.g. User Equipments (UE), mobile terminals, wireless terminals and/or Mobile Stations (MS). Wireless devices are enabled to communicate wirelessly in a wireless communications network, sometimes also referred to as a cellular communications network, a cellular radio system, cellular system, or cellular network. The communication may be performed e.g. between two wireless devices, between a wireless device and a regular telephone and/or between a wireless device and a server via a Radio Access Network (RAN) and possibly one or more core networks, comprised within the wireless communications network.
Wireless devices may further be referred to as mobile telephones, cellular telephones, laptops, or tablets with wireless capability, just to mention some further examples. The wireless devices in the present context may be, for example, portable, pocket-storable, hand-held, computer-comprised, or vehicle-mounted mobile devices, enabled to communicate voice and/or data, via the RAN, with another entity, such as another terminal or a server.
The wireless communications network covers a geographical area which may be divided into cell areas, each cell area being served by an access node such as a Base Station (BS), e.g., a Radio Base Station (RBS), which sometimes may be referred to as e.g., evolved Node B (“eNB”), “eNodeB”, “NodeB”, “B node”, or BTS (Base Transceiver Station), depending on the technology and terminology used. The base stations may be of different classes such as e.g. Wide Area Base Stations, Medium Range Base Stations, Local Area Base Stations and Home Base Stations, based on transmission power and thereby also cell size. A cell is the geographical area where radio coverage is provided by the base station at a base station site. One base station, situated on the base station site, may serve one or several cells. Further, each base station may support one or several communication technologies. The wireless communications network may also be a non-cellular system, comprising network nodes which may serve receiving nodes, such as wireless devices, with serving beams. The base stations communicate over the air interface operating on radio frequencies with the terminals within range of the base stations. In the context of this disclosure, the expression Downlink (DL) is used for the transmission path from the base station to the wireless device. The expression Uplink (UL) is used for the transmission path in the opposite direction i.e., from the wireless device to the base station.
In 3rd Generation Partnership Project (3GPP) Long Term Evolution (LTE), network nodes, which may be referred to as eNodeBs or even eNBs, may be directly connected to one or more core networks. All data transmission is in LTE controlled by the radio base station.
Multi-Antenna Techniques
Multi-antenna techniques may significantly increase the data rates and reliability of a wireless communication system. The 5th Generation (5G) technology, which is currently being developed, incorporates the use of beamforming. Beamforming may be understood as a signal processing technique which relies on combining elements in an array antenna in such a way that signals at particular angles experience constructive interference while others experience destructive interference. The beams used may typically be highly directive and provide gains of 20 decibels (dB) or more, since so many antenna elements may participate in forming a beam. An array antenna may consist of many antenna elements to achieve a large array gain. Many antenna elements may participate in forming a beam, and the beams are typically highly directive, giving beamforming gains of 20 decibels (dB) or more. Each Transmission Point (TP) may, by use of an array antenna, generate transmission of a large number of beams having different pointing direction and/or polarization. The transmission of a signal is performed over multiple antenna elements and applying individual complex weights to these antenna elements, such that the signal is basically intended for a single wireless device or terminal position. As the number of antennas increases, the energy may be focused with extreme precision into small regions in space. The result is spatial selectivity, such that beamforming may be understood as a way to transmit a signal with such narrow beams that it is intended for a single wireless device or a group of wireless devices in a similar geographical position. In 5G systems, the number of antenna elements at the transmitter and/or receiver side may be significantly increased compared to common 3G and 4G systems, as 5G systems likely will operate in higher frequencies making it feasible to place a large amount of antennas in a small physical area.
Multi-antenna techniques may significantly increase the data rates and reliability of a wireless communication system. The performance is in particular improved if both the transmitter and the receiver are equipped with multiple antennas, which results in a Multiple-Input Multiple-Output (MIMO) communication channel. Such systems and/or related techniques are commonly referred to as MIMO.
The LTE standard is currently evolving with enhanced MIMO support. In the 5th Generation (5G) technology, which is currently being developed, massive Multiple-Input Multiple-Output (MIMO) is one of the best candidate technologies for the radio physical layer. Massive MIMO, which may also be known as large-scale antenna systems and very large MIMO, may be understood as a multi-user MIMO technology where each BS may be equipped with a large number of antenna elements, at least 50, which may be used to serve many terminals that share the same time and frequency band and are separated in the spatial domain.
With introduction of the 5G technology, gigabit over-the-air mobile systems may most likely emerge. One foreseen application of the emerging 5G access is to substitute content, e.g., TV content, distribution over wireline accesses with wireless accesses. In that context, the radio connection may be represented by a non-mobility fixed point-to-point connection. Such connections may often be manifested by some sort of Fixed Wireless Terminals (FWT). FWT may be understood as wireless devices as described above, but they are limited to an almost permanent location with almost no roaming abilities. FWT are considered being substitutions for ‘Fiber To The Home’ (FTTH), a.k.a. “Fiber To The Premises” (FTTP). FTTH may be understood as a form of fiber-optic communication delivery, in which an optical fiber is run in an optical distribution network from the central office all the way to living space or a home. In everyday speech, this emerging trend is often described as deployment of “wireless fiber”.
In foreseen installations, preferred deployments to achieve sufficiently high end user performance may likely strive to maintain Line-of-Sight (LoS) between as many Customer-Premises Equipment (CPE) and Transmission Points (TPs) as possible. Typical mounting points of TPs may be at different kinds of poles in the area; for example light poles, utility pole sites, or re-using current, if any, macro cellular grid. CPEs are potentially either installed at roof-tops, being wall-mounted, outdoors, or user-deployed in some suitable indoor placement, i.e., behind some, preferably, TP-facing window. Other solutions described may be indoor customer-deployed CPEs.
Coverage from Individual Beams
To achieve the gigabit performance mentioned earlier, according to communications theory, many parallel information streams, i.e. many MIMO layers, may likely need to be conveyed. With said massive MIMO installations, a plethora of antennas, typically 128 antenna elements, may become common, and corresponding beam angles/widths may hence shrink. Given the narrower beam widths, and corresponding technical approaches to select proper directions of transmissions, the resulting “spatial resolution” at the receiving end may become very accurate compared to wide-beam macro installations, etc.
The 5G concept also brings a paradigm shift in that transmission points no longer may need to be mounted in a wide-area coverage sense, but basically installed at “street level”, near expected users.
Existing methods to provide the gigabit performance that is expected to be required in future systems may result in capacity deficiencies, as well as increased latencies of the networks.